Energy dispersive x-ray fluorescence (XRF) is a well-established technique for the measurement of elemental composition of a variety of materials. In XRF analysis, a beam of radiation is directed onto the sample to produce fluorescent emission of characteristic x-rays. The emitted x-rays are received by a detector, which responsively generates signal pulses representative of the energies of the detected x-rays. A programmable processor accumulates and analyzes the detector pulse signals to construct a plot of x-ray count rate versus energy, referred to as an energy spectrum. The energy spectrum will typically include one or more characteristic peaks corresponding to fluorescent emission by atoms of an element of interest, together with scattered radiation peaks and artifact peaks arising from various noise sources.
One type of artifact peak is known as a sum-peak, which is caused by the simultaneous or near-simultaneous reception by the detector of two or more x-rays. The processor interprets the resultant pulse as a single x-ray having an energy equal to the combined energies of the two or more individual x-rays. The presence of a sum-peak in the energy spectrum may compromise instrument performance in a situation where the sum-peak interferes with (i.e., overlaps) a characteristic peak of an element of interest. Accurate quantification of the element's concentration in the sample based on the intensity of the composite (overlapped) peak requires that the contribution of the sum-peak be accounted for. While algorithms are known in the XRF art for estimating sum-peak count rates, the use of such algorithms introduce uncertainties that increases the instrument's limit of detection (LOD) of the element of interest and adversely impacts the ability of the instrument to reliably detect the presence of the element of interest when present in low concentrations. Uncertainty arising from interfering sum-peaks in the energy spectrum is particularly problematic in view of the trend toward more stringent regulation of lead and other hazardous substances in consumer products, which imposes a need to detect the hazardous substance at progressively smaller LODs.